Perinatal exposure to estradiol results in permanent alterations in mammary development and an increased frequency of mammary dysplasia and tumors. We have previously demonstrated an enhanced in vitro hormonal sensitivity of mammary explants following perinatal estradiol treatment, determined using casein gene expression as a specific marker of mammary gland differentiation. The objective of this proposal is to define the interrelationship of hormones, mammary tumor virus (MMTV) and the chemical carginogen, dimethylbenz(a)anthracene (DMBA) on the regulation of mammary development and gene expression. The effect of perinatal estradiol treatment on MMTV expression and the response of mammary tissue to DMBA exposure will be correlated with the normal hormonal regulation of casein gene expression. These studies are designed to test the hypothesis that perinatal hormone exposure results in an increased susceptibility of mammary tissue to those agents known to initiate transformation, with the possibility of a corresponding loss in hormonally regulated differentiated function. The effects of perinatal treatment will be compared in BALB/c mouse mammary glands with or without prior MMTV infection introduced by foster nursing (BALB/cfC3H). Both casein and MMTV gene expression will be determined using fluorescent antibody and peroxidase staining techniques to detect casein protein and gp52; and specific cDNA hybridization analysis to quantitate the levels of casein mRNA and MMTV RNA in total cellular RNA extracts. A lactogenic hormone combination, i.e., prolactin, insulin and hydrocortisone, will be employed under defined conditions in mammary gland explant cultures in order to determine effects of perinatal steroid exposure at the tissue level. The response to hormone and MMTV infection will also be investigated following carcinogen administration, both in vivo and in vitro. Future studies will be directed towards studying the interaction of these agents on isolated cell populations cultured on floating collagen gels. The proposed experiments may help in elucidating the complex relationship of hormones, viruses and carcinogens in initiating mammary tumorigenesis.